Eucommia ulmoides gum-based engineering materials: fascinating platforms for advanced applications

Eucommia ulmoides gum (EUG) exhibits good rubber–plastic duality and great application potential in biomedicine, textiles, aerospace, and other fields. The extraction methods of EUG include mechanical (high-temperature cooking), alkali extraction, solvent, microbial (enzymatic hydrolysis), and comprehensive methods. However, the complicated preparation process and high cost of EUG greatly limit its application. EUG is composed mainly of trans-isoprene, and the high crystallinity of EUG at room temperature showing rigid plastics is due to the relatively regular and short identity period of its molecular chain. Through regulating the ratio of the three-phase structure of EUG (regular crystal region, completely irregular amorphous region, and intermediate region of transition pattern between the crystallized and amorphous regions), it exhibits rubber elasticity at room temperature. The application of EUG is closely related to its crystallinity and cross-linking degree. The double-bond modification of EUG by physical or chemical method can regulate its crystalline structure and cross-linking structure, so that EUG engineering materials that meet the performance requirements of multiple fields can be obtained. EUG with zero cross-linking degree is linear thermoplastic material, which is usually used in artificial limb, medical composite scaffold, composites denture soft lining, and modified plastic. EUG with low cross-linking degree is thermoelastic material, which is frequently used in the preparation of shape memory material, interfacial compatibilizer, and composite film. EUG with critical cross-linking degree is rubber-type material, which is regularly used in elastomer, self-healing material, and modified rubber. In this article, the extraction technology of EUG and its pros and cons and the structure and properties of EUG and their corresponding material states in the past 10 years were systematically discussed. The research progress of engineering materials in different states was introduced, and the effect of modification on the structure and properties of EUG was discussed. The future development direction of the materials was prospected.